Numbers k such that 2^sigma(k) == -1 (mod k).

Terms

a(0) =1a(1) =5a(2) =4097a(3) =7361a(4) =85073a(5) =658529a(6) =3999137a(7) =16777217a(8) =50281793a(9) =68544541a(10) =72281281a(11) =78202273a(12) =102931841a(13) =128459137a(14) =204786497a(15) =244622261a(16) =336392993a(17) =613750913a(18) =714155969a(19) =785432401a(20) =1008179297